Geomorphology: Earthquake

Definition

• Violent shaking of earth due to release of energy , generating seismic waves in all direction.

Earthquake Waves

1. Body Waves: Move in all direction travelling through the body of the earth
   • P Waves: Move faster. First to report on the surface of earth. Similar to sound wave and travel in all 3 medium
   • S Waves: Arrive with some time lag and travel only trough solid material.
2. Surface Waves: Last to report on seismograph and mor destructive.
   • Rayleigh Waves: A Rayleigh wave is a seismic surface wave that causes an oval shudder with no transverse or perpendicular motion. They behave like water waves.
   • Love Waves: A seismic surface wave caused by the horizontal movement of the earth during an earthquake is known as a love weave.

Associated Terms

• Hypocentre: Location where an earthquake starts just below earth’s surface.
• Focus: Location right above the hypocentre  on the earth’s surface.

Shadow Zone

Causes of Earthquake

• Faulting
• Tectonic movements
• Volcanic eruptions
• Human activities like nuclear explosion, and mining.

Measuring of Earthquakes

• Richter Scale: Based on magnitude.
• Mercalli Scale: Based on intensity

World Distribution of Earthquakes

• About 70% of earthquakes occur in the Circum-Pacific belt as the epicentre and the most frequent occurrences are along the ‘Pacific Ring of Fire’.
• Another 20% of earthquakes take place in the Mediterranean-Himalayan belt including Asia Minor, the Himalayas, and parts of north-west China.

Consequences of Earthquakes

1. Collapse of Human Property and Loss of Life
   • The deformation of the ground surface because of the vertical and horizontal movement of the earth’s crust causes huge damage and destruction to human establishments and structures.
   • For example – Syria – Turkey earthquake (2023) due to the movement of the Anatolian plate.
2. Landslides and Avalanches
   • Tremors especially in mountain areas can cause slope instability and slope failure leading to fall of debris down the slope causing landslides.
   • The huge masses of ice may fall down snow-covered peaks due to earthquakes causing Avalanches.
   • For Example: – Nepal earthquake (2015)
3. Floods
   • The earthquake can lead to devastating disturbances to dams, reservoirs and can cause flash floods.
   • For example – The Kakhovka Dam in Ukraine was breached in the early hours of 6 June 2023, causing extensive flooding along the lower Dnieper river.
4. Tsunami
   • A tsunami is a set of waves created by a disturbance, likely an earthquake, which reaches the surface of the sea. 
   • For example: – The Tsunami of 26th December 2004 of the Indian Ocean was caused by an earthquake off the coast of Sumatra.
   • Note – Other causes of tsunami are volcanic eruption, underwater nuclear explosion, and landslides.